Blow molding manufacturers blow molding process introduction

Blow molding process

Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method. The blow molding process began to be used to produce low density polyethylene vials during World War II. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow containers can reach thousands of liters, and some production has adopted computer control. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc., and the obtained hollow containers are widely used as industrial packaging containers. According to the method of making the parison, blow molding can be divided into extrusion blow molding and injection blow molding. The newly developed ones include multi-layer blow molding and stretch blow molding.

The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state), and compressed air is introduced into the parison immediately after closing the mold to blow the plastic parison. It expands and sticks closely to the inner wall of the mold, and after cooling and demoulding, various hollow products are obtained. The manufacturing process of blown film is very similar in principle to blow molding of hollow products, but it does not use a mold. From the perspective of plastic processing technology classification, the molding process of blown film is usually included in extrusion. The blow molding process began to be used to produce low density polyethylene vials during World War II. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow containers can reach thousands of liters, and some production has adopted computer control. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc., and the obtained hollow containers are widely used as industrial packaging containers.

How to properly store blow molded products?

After the plastic parts are processed and passed the inspection, they can be put into the market for sale. In the process of delivery of plastic parts, we need to pay attention to the following matters:

1. The means of transport should be clean, dry, rain-proof, fire-proof, and protected from sunlight.

2. It should not be severely impacted or thrown during transportation, and should be handled with care when transferring to prevent beating and kneading.

In addition, we put forward the following storage requirements for processed plastic parts that have not been shipped from the factory or processed plastic parts that have not been sold:

1. Plastic parts should be kept in a well-ventilated warehouse, there is no corrosive gas around, and avoid high temperature heat sources and fire sources.

2. The storage period is one year, and the quality inspection department will review it once every six months.

What is the temperature of the blow molded product?

Many blow molding manufacturers will ask and encounter various questions about temperature, such as: Is blow molding technology different from injection molding? What is the temperature of blow molding products? The products blown out of plastic simply crack. What is the factor? and many more.

The melt temperature of blow molding products has a significant impact on the molding performance and product performance. The advancing temperature can reduce melt strength, improve fluidity, reduce screw power consumption, and reduce the adverse effect of melt elasticity on product performance. However, when the temperature is too high, it is difficult to maintain the shape of the product, extending the cooling time of the product, and possibly thermal degradation. Blow-molded parisons require molding at the lowest possible temperature to ensure that the parison has a high melt strength. The best processing temperature is generally determined by experiments, which mainly depends on the function of the polymer and the variety, shape and standard of the product.

The temperature control of the storage chamber is also a problem, as some polymers can degrade during processing, especially if the processing temperature is high or the melt is lingered in the storage chamber for a period of time during intermittent blow molding. In addition, blow molding process grade polymers contain a variety of additives that form by-products during the melting process. These degradation products or by-products will accumulate in the flow channel of the machine head, causing stripes on the surface of the parison, affecting the appearance and function of the product. Therefore, keeping the machine head clean is an important condition for blow molding high-performance products.

Factors Affecting Blow Molding Machine Forming

There are various factors that affect the blow molding process, and various reasons may lead to the failure of the blow molding machine to produce products. In order to facilitate everyone to deal with these problems in actual operation, this article will list the blow molding machine molding factors one by one. , in order to resolve the situation.

1. The temperature of the parison and the speed of extrusion, the temperature affects the quality of the hollow product, the uniformity of the longitudinal wall thickness, and the production efficiency, so pay attention to maintaining the uniformity of the melt temperature, adjust the temperature appropriately, and shorten the cooling time. If the temperature of the parison is too high and the extrusion speed is slow during the production process, the parison will easily sag and cause uneven longitudinal thickness of the parison. This operation may lead to prolonged cooling time and the product cannot be formed.

Not only that, the temperature of the parison is too low, the mold expansion is serious, and the length shrinkage will occur, and the increase of the wall thickness will reduce the surface quality of the parison, resulting in the appearance of flow marks. There is a roll-up phenomenon.

2. Blowing pressure and blowing rate, parison inflation uses compressed air to apply air pressure to the parison to expand and refine the nasal cavity of the iron mold, and at the same time, the required shape and pattern are formed by the cooling of the compressed air. The elimination of blowing pressure is related to the type of product, temperature, wall thickness, and volume. For low viscosity and small volume, choose low blowing pressure, otherwise, choose high blowing pressure.

The blowing rate is the solvent rate of the air. When the blowing rate is high, the time between blowing molding is short, and the product has a good uniform surface quality. It should be noted that when the rate increases, the air will generate local sugarcane farmers at the inlet, causing indentation and breaking the parison, making it impossible to blow. swell.

3. Mold temperature, mold temperature should be kept evenly distributed to ensure uniform cooling of products, affecting the thickness of plastic products. Generally, the temperature of small molds is low, about 40°C lower than the softening temperature.

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